Minimization of edge cracking during hot rolling of silicon-tin bronzes

Abstract

Particular copper base alloys consisting essentially of silicon, tin and mischmetal are disclosed which exhibit improved resistance to edge cracking during hot working operations. Various other elements such as chromium, manganese, iron and nickel may also be added to the alloy to increase the strength properties of the alloy without affecting the hot workability improvement brought about by the mischmetal addition to the copper-silicon-tin base.

What is claimed is: 
     
       1. An alloy which exhibits high resistance to edge cracking during hot working, said alloy consisting essentially of 2 to 4.0% by weight silicon, 0.5 to 3.0% by weight tin, with a total silicon plus tin content to less than or equal to 6.0% by weight, 0.005 to 0.1% by weight mischmetal, balance copper. 
     
     
       2. An alloy as in claim 1 wherein an element selected from the group consisting of chromium, manganese, iron and nickel in amounts up to 0.5% by weight in total is added to said alloy. 
     
     
       3. An alloy as in claim 1 which consists essentially of from 2 to 3.5% by weight silicon, 0.5 to 2.5% by weight tin, with a total silicon plus tin content of less than or equal to 5.5% by weight, 0.01 to 0.05% by weight mischmetal, balance copper. 
     
     
       4. An alloy as in claim 3 wherein an element selected from the group consisting of chromium, manganese, iron and nickel in amounts up to 0.5% by weight in total is added to said alloy. 
     
     
       5. A process for forming an alloy which exhibits high resistance to edge cracking during hot working, said process comprising: (a) providing a copper base alloy which consists essentially of 2 to 4.0% by weight silicon, 0.5 to 3.0% by weight tin, with a total silicon plus tin content of less than or equal to 6.0% by weight, 0.005 to 0.1% by weight mischmetal, balance copper;   (b) hot working said alloy from a starting temperature in excess of 650° C. up to within 20° C. of the solidus temperature of the alloy, with a temperature at the completion of the hot working step in excess of 400° C.;   (c) cold working the alloy to the desired gage; and   (d) annealing the alloy at a temperature between 450° and 600° C. for from 1/2 to 8 hours.   
     
     
       6. A process as in claim 5 wherein an element selected from the group consisting of chromium, manganese, iron and tin in amounts up to 0.5% by weight in total is added to said alloy. 
     
     
       7. A process as in claim 5 wherein prior to hot working the alloy is heated at a temperature between 600° C. and the solidus temperature of the alloy for at least 15 minutes. 
     
     
       8. A process as in claim 5 wherein the alloy is annealed at a temperature between 450° and 600° C. for 1/2 to 8 hours immediately following said hot working. 
     
     
       9. A process as in claim 5 wherein said cold working and annealing steps are repeated at least once. 
     
     
       10. A process as in claim 5 wherein the annealing temperature is between 450° and 550° C. and the annealing time is between 1/2 and 2 hours. 
     
     
       11. A process as in claim 5 wherein the product formed from the processing steps is formed into a part and said part is heat treated at a temperature between 150° and 400° for from 15 minutes to 8 hours.